Management of the operation of a turbocharged engine requires in particular knowledge of the change in value of the atmospheric pressure, in particular in order to allow an estimate of the boost pressure provided by the turbocharger.
At present, normally atmospheric pressure is determined by means of an external pressure sensor.
However for economy reasons, techniques have been proposed—as described in patent applications US 2009/0132148, DE 10 2008 000934A1 and FR 2 853 012—allowing determination of atmospheric pressure without requiring a specific pressure sensor.
As described in these patent applications, these techniques are designed to allow determination of atmospheric pressure during opening and closure respectively of the butterfly valve situated in the engine air intake line, and thus the atmospheric pressure can be determined in particular on each change of ratio. Document DE 10 2008 000934A1 relates to a method for determining atmospheric pressure of a turbocharged engine in operation, by using a difference in atmospheric pressure Δpatm which is a function of Δh, i.e. the difference in altitude covered by the engine between two points of determination of the atmospheric pressure; the teaching in this document is to use the engine deceleration to determine atmospheric pressure. It is however indicated that when the turbocharger is activated, this together with the pressure sensor PUT can no longer be used to detect atmospheric pressure.
In addition, patent application FR 2 853 012 proposes, when the butterfly valve is lying in an intermediate position between its closed position and its open position during a relatively long time interval, corresponding to a partial load state of the engine, calculating the atmospheric pressure in an open loop by reducing the value of the latter by a given value per time interval. It is in fact assumed in this method that the positioning of the butterfly valve is obtained when the vehicle climbs an incline, with a consequent, corresponding reduction in atmospheric pressure.
This method of determining atmospheric pressure in an open loop has however proved unreliable and leads to significant errors.